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The diode is between drain and source on fet.? Source is ground.can you explain why it works??
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There are two different mechanisms for reverse breakdown in diodes: zener and avalanche.? Generally diodes with low reverse breakdown are in the zener mode and diodes with higher breakdown voltages are avalanche.?? I think the "dividing line" is somewhere around 5 volts.?
That said there are many diodes made and used because of the reverse breakdown.? Very seldom does the part catalog point out the difference.? And in 99% of the time that's not important in the use of the diode.
Now back to the transmitter and high SWR.? There is a video showing the rig survived when connected to a short cable and SWR measurement device.? In this case the "load" on the transmitter is an open. Now, if one was to connect a 1/4 wavelength of cable ( simply just a short) the transmitter would still see really high VSWR, but it would be 0 Ohms.
Different loads will have different effects on the transistor.?
Now back to the photos showing the diode.? I don't have a schematic and PC layout, but I think maybe the diode is not connected directly to the FET, but to VDD with a coil or choke between that point and the actual FET. In this case, it would prevent the reflected RF signal from raising the FET voltage into the danger zone.
At this time, I have enough radios that I'm not planning on another.?
On the subject of "too many radios".? There was a recent microwave contest.? Because I got bonus multipliers for QSO's on 24 and 47 GHz, I finished in the top 3 individual scores in the country.?
On Tuesday, June 11, 2024 at 10:17:55 AM PDT, Jeff Reagan <jeffreagan@...> wrote:
It gets back to the question: is the Avalanche Breakdown characteristic of the FET more delicate than that of a 1 watt zener. Maybe the 1 watt zener is tougher than the FET. Counterintuitive results are everywhere.
On Tue, Jun 11, 2024 at 10:12?AM Doug Hendricks via <ki6ds1= [email protected]> wrote: Doesn't Hiroki's video disprove that?
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It gets back to the question: is the Avalanche Breakdown characteristic of the FET more delicate than that of a 1 watt zener. Maybe the 1 watt zener is tougher than the FET. Counterintuitive results are everywhere.
On Tue, Jun 11, 2024 at 10:12?AM Doug Hendricks via <ki6ds1= [email protected]> wrote: Doesn't Hiroki's video disprove that?
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The zener in the video is connected across the FET, between source and drain. That zener is definitely not subjected to RF AC output voltage.
On Tue, Jun 11, 2024 at 10:06?AM Jeff Reagan via <jeffreagan= [email protected]> wrote: There's another possibility: the zener is so weak, it blows open the instant the transmitter comes on.
Here is an empirical proof to show how a single 1N4756 zener diode actually protects against high SWR.?
I ordered a bag of 10 1N4756As. I won¡¯t need all of them. Anyone who needs one would be welcome to get it from me on Friday (if they arrive before then, if not another Friday.)
Hiroki AH6CY
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?
My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
Doesn't Hiroki's video disprove that?
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There's another possibility: the zener is so weak, it blows open the instant the transmitter comes on.
Here is an empirical proof to show how a single 1N4756 zener diode actually protects against high SWR.?
I ordered a bag of 10 1N4756As. I won¡¯t need all of them. Anyone who needs one would be welcome to get it from me on Friday (if they arrive before then, if not another Friday.)
Hiroki AH6CY
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?
My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
Here is an empirical proof to show how a single 1N4756 zener diode actually protects against high SWR.?
I ordered a bag of 10 1N4756As. I won¡¯t need all of them. Anyone who needs one would be welcome to get it from me on Friday (if they arrive before then, if not another Friday.)
Hiroki AH6CY
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On Jun 11, 2024, at 09:17, Jeff Reagan <jeffreagan@...> wrote:
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My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
There are pictures of both rigs with diode installed at the beginning of this thread.?
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My guess is, it isn't across the RF output.
Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
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Guys, first of all I am not an engineer.? ?Please go to trusdx forum and do a search for 1n4756a.? Read the posting by Sars.? He says no I'll effects, i.e. spurious or harmonics generated.? ?Our FT8 kit uses a 1n4756a for protection and we have sold over 1000 of them and never had a blown BS170 reported.? Something the trusdx guys can't say.? Why don't one of you who has a trusdx and test equipment, install the zener and measure it.? ?
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Oops. I tend to give people the benefit of the doubt. It begs the question, where was that zener really connected?
Cooy and paste from above: "I? strongly encourage you to install a 1N4756A diode between rf and ground."
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I built a 6 meter rig back in high school.? I had a WA8 call and collected QSL cards from 20 states.? Then I move to CA and channel 2 TV brought that to an end.
Last year, I got motivated to get back on the Magic Band. While thinking about antennas, a local ham said he was selling his 5 el Cushcraft. Virtually the same as I once had. I put it on a 30 ft push up.? I started with my 705.? Then I found the 706 that had been sitting in a box for some years.? After several calls to West Mountain tech support, I got both rigs to do FT-8.
This was just in time for the '23 June VHF contest.? I knew from past experience that 6 tends to be good around the summer solstice and sometimes good around the winter solstice.? I couldn't believe the number of simultaneous decodes I was getting.
Now the "not so good part".? Virtually all activity on 6 is now FT-8.? I've tried numerous times without success to make any QSO's on SSB or.
Just now, I am in OR.? Grandson graduated HS this weekend.? Hope others had fun during the past contest.
On Tuesday, June 11, 2024 at 12:59:20 AM PDT, David via groups.io <dkvarn@...> wrote:
...meters, that is. I have a vintage Heathkit SB-110A 6-meter transceiver that I purchased c. 2000 and am considering selling on ePay. I was hoping to get it going for the first time this past weekend (I have a pretty good rig backlog) and using it on SSB during the ARRL VHF Contest. I did the usual vintage rig prep. Unfortunately the transmit section seem kaput, but the receive section seems to be working.?
I did not hear the expected SSB signals--did any of y'all? I did hear tones around 50.16 and 50.31 MHz--I understand the latter is FT8, yes? As to the former, online info indicates that it is used by Radio Scouts / Jamboree on the Air, JOTA. Anybody familiar with that?
A member recently mentioned that to test an SSB transmitter, one could use a phone app to generate FT8 audio, play the phone's audio into the mic of the transmitter and use PSK Reporter as a reverse beacon.?
How about the inverse, i.e., play FT8 audio through an SSB rig's speaker and use a phone app to listen and decode the FT8 signal (?) I could more fully verify the SB-110A's receiver operation that way.
I'm also thinking of doing a video including the received FT8 audio and posting the video in the eBay listing.
Thanks, and best, --David KM6RI
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I totally agree.? With the one diode as originally proposed, it would clip the waveform and generate harmonics.
On Tuesday, June 11, 2024 at 01:12:22 AM PDT, David via groups.io <dkvarn@...> wrote:
My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
https://resources.pcb.cadence.com/blog/2020-what-happens-when-you-connect-zener-diodes-in-series
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Cooy and paste from above: "I? strongly encourage you to install a 1N4756A diode between rf and ground."
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David: you would be correct, if the zener were placed across the RF output. Then it wouldn't work at all. The zener would probably blow right away.
I got the impression this zener was placed in parallel with the FET, to clamp the peak voltage.?
AC voltage can't appear across a FET. FETs have both an Avalanche-Mode breakdown characteristic (resembling an internal power zener), and an intrinsic diode (also resembling a power zener). This internal parasitic diode is antiparallel with the switching part of the device.
My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
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My understanding is that a Zener diode "Zeners" in the reverse direction, but acts as a regular silicon diode in the forward direction, i.e., with a nominal 0.7 V forward drop. Since the transmitter output device "sees" AC, is a single shunting Zener diode appropriate? Wouldn't two Zeners back-to-back (i.e., in series with opposing orientations) be better? See, e.g., below.
Best, --David KM6RI
https://resources.pcb.cadence.com/blog/2020-what-happens-when-you-connect-zener-diodes-in-series
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...meters, that is. I have a vintage Heathkit SB-110A 6-meter transceiver that I purchased c. 2000 and am considering selling on ePay. I was hoping to get it going for the first time this past weekend (I have a pretty good rig backlog) and using it on SSB during the ARRL VHF Contest. I did the usual vintage rig prep. Unfortunately the transmit section seem kaput, but the receive section seems to be working.?
I did not hear the expected SSB signals--did any of y'all? I did hear tones around 50.16 and 50.31 MHz--I understand the latter is FT8, yes? As to the former, online info indicates that it is used by Radio Scouts / Jamboree on the Air, JOTA. Anybody familiar with that?
A member recently mentioned that to test an SSB transmitter, one could use a phone app to generate FT8 audio, play the phone's audio into the mic of the transmitter and use PSK Reporter as a reverse beacon.?
How about the inverse, i.e., play FT8 audio through an SSB rig's speaker and use a phone app to listen and decode the FT8 signal (?) I could more fully verify the SB-110A's receiver operation that way.
I'm also thinking of doing a video including the received FT8 audio and posting the video in the eBay listing.
Thanks, and best, --David KM6RI
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Chelegence MC-750 vertical
Does anyone have any experience with this antenna?? I would love to hear about it.? Doug
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Re: How do I delete a group
I knew it.? After a couple of hours fiddling, I realized that you probably can't do it on the phone, and I was right.? Went to laptop and solved problem.? Sorry for troubling the group.? Doug
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I have several groups.io groups that I haven't used in a long time.? ?How do I delete them
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Jeff Reagan
David